It is common during wellbore operations to circulate fluids downhole. Sometimes fluid circulation is conducted for lubrication or for wellbore treatments, such as cleaning and stimulation, including fracturing.
Wellbore strings are sometimes employed to convey fluids downhole. For example, connected tubulars or continuous strings such as coiled tubing may be employed to form conduits that may be run into a well. Fluids may be conveyed through the inner bore of the strings from surface to a selected point in the well. Ports and valves may be employed to permit selective access between a wellbore tubing string inner diameter and an annulus about the string.
In some embodiments, packers may be employed in association with the string to permit focused delivery of fluids. For example, FIG. 1A shows a prior art straddle packer 10 that is deployed on string 11, in this case of coiled tubing, including attached or integral thereto a tubular body 12 with a port 14 through its wall. Fluid may be delivered, arrows F1, from the tube inner diameter 12a, through the port, to the annulus 16 between the tube's outer surface 12b and the wellbore wall 18. An annular packer 20 encircles the tube on one side of the port and another annular packer 22 encircles the tube on the opposite side of the port. The packers, therefore, straddle the port and are configured such that together they ensure that any fluid exiting the port is maintained in the area between the packers.
The straddle packer of FIG. 1A is being employed in a standard operation of injecting fluid into a formation 23 accessed by the wellbore wall. In this case, the wellbore is lined with a liner 24 and cement 26 and the fluid passes through a hole 28, such as a perforation or port in the liner and cement before reaching the formation. In such a process, fluid in the string inner diameter 12a, both that from run in and newly introduced fluid from pumping, will be forced from the string into the formation. The process of forcing non-intended, residual fluids into the formation is termed bull heading and sometimes results in formation damage and is wasteful.
Another straddle packer operation is shown in FIG. 1B. FIG. 1B illustrates a process for addressing sand accumulation during straddle packer use. In particular, during use of straddle packer, sometimes sand 30 accumulates uphole of the upper packer, in this illustration packer 20. If it is desired to remove that sand, for example, when the tool becomes sanded in, fluid F2 is pumped down the annulus, past the upper packer (a downwardly facing cup seal as shown) to force the sand from above the packer, through port 14, and into string 11. This process sometimes experiences difficulties, especially if the sand is packed in around the upper packer. If the sand cannot be removed, the straddle packer may get stuck in the well. In such a situation, the string may have to be removed from the well and a fishing operation conducted to remove the straddle packer.